Conventional gas turbine engines that utilize can annular combustors include combustor cans to generate hot combustion gases, a transition duct to receive the hot gases and deliver them to a first row of guide vanes, where the guide vanes turn and accelerate the hot gases so they will be at a proper orientation and speed for delivery onto a first row of turbine blades. In these conventional arrangements the combustor can and the transition are angled radially inward but are otherwise aligned with the engine axis. Air is compressed by an axial compressor and slowed in a diffuser from which it then flows primarily axially into a plenum defined by the midframe. Once in the midframe the compressed air flows radially outward and back upstream toward combustor can inlets. Since the diffuser outlet and the combustor cans are concentric with the engine axis the compressed air flow is essentially radial and axially aligned with the engine axis, thus having no significant circumferential velocity.
Advances in gas turbine engine technology have yielded one configuration for a combustor arrangement where the combustor cans are not axially aligned with the engine axis. Such a configuration is described in U.S. Pat. No. 8,276,389 to Charron et al. and is incorporated herein in its entirety. Instead, in this configuration the hot gases are generated in the combustor cans and travel along respective flow paths and are delivered directly onto the first row of turbine blades without the need for the first row of vanes to turn and accelerate the hot gases. This is possible because the hot gases leave the combustor cans along a path that is already properly oriented for delivery directly onto the first row of turbine blades. Also, between the combustor cans and the first row of turbine blades each gas duct accelerates its respective flow of hot gases to the proper speed. Thus, the combustor arrangement dispenses with the need for the first row of turbine vanes.
In order to ensure the hot gases are properly aligned when leaving the combustor cans the combustor cans must align with a desired turbine flow path. An axis of this desired flow path may be aligned with a plane that is perpendicular to a radial of the engine axis and offset from the engine axis so that the flow leaving the combustor cans has a significant circumferential velocity that is required to drive the rotation of the first row of turbine blades. This arrangement is a significant departure from any previous arrangement, where the combustor cans are aligned with the engine axis, and hence there is room in the art for optimization.